The long term goal of the P.I. is to determine the basis of ionizing radiation mutagenesis (IRM). This project is a REVISION of an earlier proposal (1 r01 CA55789-01A1) and its goal is to determine in Escherichia colt by DNA sequencing analysis the mutational spectrum [ile. the kinds and locations of dominant lac1 (lacId) mutations] induced by gamma-irradiation (doses yielding about 5% survival and also doses that do not fully induce SOS) the effect of various gamma-irradiation gassing conditions on the mutational spectrum (i.e. N2 air N-) or N2+glycerol) the effect of hydrogen peroxide scavenging procedures on the gamma-radiation mutational spectrum (irradiation in the presence of extracellular catalase and the presence of oxyR2, a mutation that causes the overproduction of catalase. , etc.): and the effect of various DNA repair mutations on the gamma-radiation mutational spectrum (umuC. polB. and a xth nth nfo triple mutant). The ultimate goal is to try to associate specific mutations with specific kinds of DNA damage and repair processes. The completion of the following specific aims will require the production of about 20 new lacld mutational spectra and the sequencing of about 7000 new mutations (beyond data already obtained with the Shannon award). The specific aims of this project are; (1) To determine the specific nature of umuC-dependent and umuC- independent IRM (irradiation under N2). and the putative involvement that DNA polymerase II plays in umuC- independent IRM (irradiation under N2) and the putative involvement that DNA polymerase II plays in umuC-independent IRM. (2) To determine the lac1d IRM that is specifically enhanced by "high dose" irradiation in the presence of O2 to elucidate the specific role of error-free repair in preventing IRM and ultimately to associate O specific IRM and repair with O specific damaged bases (3) To determine the role of hydroxyl radicals on gamma-radiation-induced laced mutational spectra cells will be irradiated under N2+ glycerol (a hydroxyl radical scavenger) or under N2O (which doubles the yield of hydroxyl radicals and scavenges hydrated electrons) for comparison with the same cells irradiated under N2 and ultimately an attempt will be made to associate specific IRM with specific DNA damage. (4) To determine mutational spectra induced by a small gamma-radiation dose when SOS repair is not fully activated and also when it is maximally activated (same dose but using a recA703 lexA51 sulA strain carrying pSE117, which carries the umuDC genes). (5) To determine the gamma-radiation mutational spectrum under all four gassing conditions target that is transferred from a nonmutable cell to a wild-type recipient so that the identity of the damaged bases that induce mutations can be determined and compared with mutational spectra obtained above. Health relatedness Elucidation of the genetic and radiochemical bases of ionizing radiation mutagenesis will be valuable towards understanding radiation carcinogenesis.